JPH06215921A - Method for producing calcined powder for ferrite - Google Patents

Abstract

(57) [Summary] [Purpose] Stable production of calcined ferrite powder with good formability in actual operation. [Structure] Moisture and air are eliminated by compressively dehydrating the wet mixed ferrite raw material slurry or cake at a pressure of 50 to 200 kg / cm ² . Dry this,
The ferrite calcined powder obtained by calcination and pulverization has a low porosity and good moldability. Further, since the particle size dependency of the formability is reduced, stable operation can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for stably producing a calcined powder for ferrite, which can easily obtain a high molding density, that is, has good moldability.

[0002]

2. Description of the Related Art A soft ferrite used for a power transformer, a deflection yoke, etc. and a hard ferrite used for a permanent magnet are mixed with primary raw materials, and calcined and crushed so-called calcined powder is kneaded with a binder to form granules having various shapes. It is manufactured by molding in a specific atmosphere and firing in a specific atmosphere. In the molding process, uniaxial pressure molding in which granules in a mold are compressed from above and below is generally used in consideration of mass productivity. If a calcined powder having poor formability is used, a high forming load is inevitably required, and accidents that damage the mold often occur. Further, the higher the molding density is, the smaller the shrinkage factor at the time of firing is, so that the dimensional accuracy of the product is improved. Therefore, obtaining a high molding density with a low molding pressure, that is, improving the moldability is an important issue that can be expected to reduce the manufacturing cost and improve the yield.

Various methods have heretofore been considered for improving moldability. For example, a method using an aqueous emulsion of polybutadiene modified epoxy resin as a binder in JP-A-59-78974, JP-A-2-208.
A method of surface-treating a calcined powder with an organometallic compound disclosed in Japanese Patent No. 257 is known. However, the surface modification of the calcined powder is limited and is not an essential solution.

[0004]

SUMMARY OF THE INVENTION The present invention improves the formability of the calcined ferrite powder by lowering the porosity in the calcined powder, and essentially solves the problem of die damage. At the same time, it becomes possible to manufacture a calcined powder that exhibits stable formability with respect to operating fluctuation factors.

[0005]

According to the present invention, a wet-mixed ferrite raw material slurry or cake is pressed at a pressure of 50 to 200.
A method for producing a calcined powder for ferrite, which comprises calcination and pulverization after compression dehydration within a range of kg / cm ² .

The details of the invention will be described below. In a general method for producing a calcined ferrite powder, first, raw materials such as iron oxide are wet-mixed with an attritor, a ball mill or the like, and dehydrated with a filter press or the like to make a cake. Next, the cake is dried, crushed, and calcined in a rotary kiln or the like. A method is also known in which a cake is formed with a roll compactor or the like, dried, and calcined. In the pulverizing step, a method of using dry pulverization (coarse pulverization) using a vibration mill, atomizer or the like and wet pulverization (fine pulverization) using a ball mill, attritor or the like is generally used.

[0007] As a result of intensive study of the relationship between the calcined powder production process and the formability of the calcined powder, the inventors have found that the cake obtained by filtering the mixed raw material slurry is compressed and dehydrated at a higher pressure to achieve good molding. It has become clear that high performance and high operational stability can be obtained. That is, by compressing and dehydrating, the entire cake is isotropically compressed, and moisture and air left in the cake are removed. Similar results can be obtained by directly compressing and dehydrating the slurry with a tube press or the like. Compression pressure when this is suitably in the range of 50 to 200 kg / cm ^2, preferably it is more effective in the range of 100 to 200 kg / cm ^2. If it is less than 50 kg / cm ² , the air in the cake cannot be sufficiently removed, and the desired effect cannot be obtained. On the other hand, if it exceeds 200 kg / cm ² , the porosity does not change, and a compression pressure exceeding this value is meaningless.

Further, by compressing the cake, the number of contact points between the raw material powders increases, so that sintering is promoted during calcination. Further, since the powder is compacted and the granule strength is improved, it is possible to reduce the adhesion of the granule disintegration powder, which is the main cause of heat transfer inhibition, to the inner wall surface of the kiln. Therefore, in the calcination step, it is possible to stably produce a dense unground calcinated powder having a low porosity for a long period of time. Here, it is desirable to set calcination conditions such as temperature so that the specific surface area of the unground calcinated powder is 0.4 to 0.8 m ² / g. Specific surface area 0.4 m ²
If it is less than / g, the sintering proceeds too much, and it becomes difficult to pulverize in the next step, which is not preferable. Conversely, the specific surface area is 0.8 m ² /
If it exceeds g, it does not become a fine unpulverized calcined powder, and the effect of compacting the powder cannot be obtained.

In order to obtain a good moldability, the inventors reduced the number of coarse particles of about several μm as much as possible, and made them 0.1 μm.
We have found that it is important to suppress the generation of ultrafine powder. In order to satisfy these contradictory conditions, it is necessary to thoroughly examine the crushing conditions and to carry out pinpoint operation management, and it is very difficult to continue stable operation. However, due to the compaction of the raw material mixed powder, which is the point of the present invention, even if coarse particles of about several μm remain after the pulverization, the porosity is low and therefore the formability is not extremely deteriorated. That is, since the dependence of the calcined powder on the particle size distribution of the formability becomes small, it becomes possible to produce a calcined powder with stable formability. Therefore, in the crushing process, if you do not generate even the ultrafine powder that causes lamination during molding,
Does not require strict particle size distribution management. Desirably, the specific surface area is 3.0 m ² / g or less, and the average particle size is 1.5 to
If pulverized to about 3.0 μm, it is possible to obtain a stable calcined powder having good moldability.

[0010]

EXAMPLE Fe ₂ O ₃ , MnO, and ZnO are mixed in a molar ratio of 5
Iron oxide, manganese carbonate, and zinc oxide were wet-mixed with a ball mill so that the ratio was 3:35:12, and then vacuum filtration was performed to form a cake having a water content of 28%. This cake was wrapped in a filter cloth, compressed and dehydrated at a pressure of 50 to 200 kg / cm ² using a hydraulic press, dried and crushed, and then dried in the air at 105
It was calcined at 0 ° C. for 1 hour. Wet these with a wet ball mill
After pulverizing by changing the pulverizing time in the range of 32 hours, a predetermined amount of PVA aqueous solution was added, and the mixture was kneaded, granulated, and 1 ton /
It was molded into a pellet having a diameter of 10 mm at a pressure of cm ² , and the molding density was measured. Mn-Zn thus obtained
The relationship between the average particle size of the calcined ferrite powder and the molding density is shown in FIG. For comparison, the wet-mixed slurries were dried as they were, and then calcined, pulverized, and molded under the same conditions, and the results are also shown in FIG.

[0011]

As is apparent from FIG. 1, the present invention improves the formability of the calcined powder by compressing and dehydrating the raw material mixed slurry or cake, and further reduces the particle size dependency of the formability. In addition, even with respect to operational fluctuations in the calcination and crushing processes,
It is understood that it becomes possible to produce a calcined powder with stable moldability.

[Brief description of drawings]

FIG. 1 is a diagram showing behaviors of an average particle diameter and a molding density with progress of pulverization when a compression dewatering pressure of a cake is changed.

Claims (1)

[Claims] 1. A method for producing a calcined powder for ferrite, which comprises subjecting a wet mixed ferrite raw material slurry or cake to compression dehydration at a pressure of 50 to 200 kg / cm ² , calcination and pulverization.